In the present state of the art relating to the electrical simulation of acoustic phenomena, it is known to simulate acoustic phenomena taking place in installations having a constant volume.
This volume V is thus compared with a disconnected capacitor having a capacitance C, which has been charged with a quantity Q of electricity by applying a potential difference e, itself similar to the pressure p of the gas enclosed in the volume V.
Most of the thermodynamic expansions to which the invention relates do not however take place in a constant volume and it is an object of the invention to simulate the thermodynamic expansion of a gas in a chamber having a variable volume, if necessary with flow into and/or out of the chamber.
In the case of an isothermal expansion of gas in a chamber of variable volume, but without flow, the relationship between the instantaneous volume V (t) of the chamber and the instantaneous capacitance C (t) of a variable capacitor can be maintained at all times. This may be expressed by the similarity existing between Mariotte's law: EQU P(t).times.V(t)=constant
and the theoretical formula which would express the constant nature of the quantity Q of electricity stored in a disconnected capacitor whose capacitance C (t) varies over a period of time, which would vary the potential difference e (t) over a period of time existing between the capacitor plates: EQU C(t).times.e(t)=Q=constant.
Under these conditions, an isothermal transformation could thus be simulated by the use of a variable capacitance capacitor.
However, in practical terms, such a simulation would be difficult to achieve for several reasons.
A first difficulty resides in that the simulation of cyclic phenomena due to the operation of a rotary machine such as an engine or compressor would require a speed of variation of the capacitance of the capacitor which is incompatible with currently known means for the mechanical variation of such a capacitance.
Another difficulty results from the fact that if it is possible to charge a capacitor progressively, the discharge resulting from a decrease in its capacitance for example could be violent.
Finally, the similarity between the interdependence of the pressure and volume of a gas and the interdependence between the capacitance of a disconnected capacitor and the instantaneous potential difference between its terminals is limited to the case of an isothermal expansion of the gas, without any flow of gas from the chamber containing it, which is quite inadequate for expressing all the possible expansions of the gas.